This invention relates to a turbomachine rotor arrangement and more particularly to a lashing or tying construction for turbine rotor blades.
As rotation machines such as a pressure compressor have been required to be gradually driven at higher speeds, steam turbines for driving them have also been required to be operated at higher rotational speeds. Turbine blades of such high speed turbines are exposed in a state that extremely large centrifugal force occurs thereon, so that high stress is generated on stress concentration portions such as at blade fixing portions on a rotor wheel.
In order to avoid stress concentration on the blade fixing portions at the high speed, recent high speed steam turbines have been made with the periphery of the circumference of a cylindrical member cut or machined to be formed with blade portions integral (one-piece homogeneous material) with a rotor wheel portion. Turbines with such construction are advantageous in strength, because large stress does not occur on the blade fixing portions.
The latest turbines, however, are needed to drive rotation machines at a further higher speed and under a higher load.
Since the blades integrally formed with the rotor wheel portion are not favorable arranged for mechanical vibration damping effects, the logarithm damping rate becomes equal to that of the rotor member itself.
Accordingly, said blades exhibit a tendency for vibration stress to become extremely large in comparison with usual separate blades assembled on a rotor wheel, because the vibration damping effect is drastically reduced.
Under this circumstance it is required to effectively damp the vibration at the high speed for blades, especially blades integrally formed with a rotor wheel portion.
Prior arrangements have been provided for lashing adjacent turbine blades together to reduce or damp vibration effects during operation. However, these prior arrangements, as exemplified by U.S. Pat. Nos. 3,527,546 to Zeman, and 3,795,462 to Trumpler, Jr., as well as Canadian Pat. No. 752,203 to Jensen, positioned the tie connections at a constant radial height on adjacent blades. The present invention is directed at improving such vibration damping arrangements.
An object of the invention is to provide a turbomachine rotor arrangement which can effectively restrain the vibration of the blades.
Another object of the invention is to provide a turbomachine rotor arrangement which can effectively restrain, at the high speeds, the vibration of blades which are integrally formed with a rotor wheel from one rotor member.
Another object of the invention is to provide a turbomachine rotor arrangement which can damp circumferential direction vibration, blade arrangement direction vibration, and torsional vibration.
Another object of the invention is to simplify the rotor and blade arrangement so as to make the manufacture thereof more economical.
An important feature of the invention is the provision of a turbomachine rotor arrangement having a rotor wheel and blades thereon with tie means for interconnecting adjacent blades, comprising a plurality of blades respectively defining tie holes wherein adjacent blades define tie holes with the radial distances between each center of said holes and the circumferential surface of the rotor wheel being different, and with tie means for interconnecting said plurality of blades, said tie means being disposed in said tie holes so as to be acted upon by different amplitudes of vibration thereon at respective adjacent blades during rotation.
This arrangement of the tie holes at different radial heights on the respective adjacent blades assures that the tie means provide a damping effect on each of the: (i) circumferential direction blade vibration, (ii) the blade arrangement direction blade vibration, and (iii) the torsional blade vibration.
In certain particularly preferred embodiments, the rotor and blades are formed integrally with one another from a unitary piece of material.
In some preferred embodiments, the tie means are formed as rigid straight tie pins extending through tie holes in three or more adjacent rotor blades with a small clearance between the tie holes and the tie pins, whereby centrifugal forces during rotation frictionally lock the tie pins to the blades.
In other preferred embodiments, the tie means are formed as rigid straight tie pins extending through tie holes in three or more adjacent blades, with the blades and tie pins being welded together at the tie pins.
These and further objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.